Gage-control apparatus



July 4, 1967 M. FERACI 3,328,987

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INVENTOR. MICHAEL FERA Cl Agent United States Patent 3,328,987 GAGE-CONTROL APPARATUS Michael Feraci, Pittsburgh, Pa., assignor to Crucible Steel Company of America, Pittsburgh, Pa., a corporation of New Jersey Filed May 14, 1964, Ser. No. 367,468 2 Claims. (Cl. 72-8) This invention relates to apparatus for rolling metal and, in particular, to improved rolling-mill apparatus capable of hot-rolling different metals to an accurate, uniform preselected thickness.

In the steel industry, it is common practice to use, for example, a multi-stand tandem finishing train to reduce a sheet bar about 1 inch thick and 40 inches wide to a hot band about 0.080 inch thick. Obtaining a hot band having a thickness which is uniform within desired preselected limits poses a difiicult technical problem, even under relatively ideal conditions, such as when a great number of slabs of the same relatively soft, low-carbon steel are to be rolled. In such a case the problem of adapting the mill to handle, accurately and without undue efforts of re-adjustment, steels of different kinds, with consequently different responses to hot rolling, is not encountered; there are, however, the problems of off-gage head ends, off-gage tail ends, skid marks, and thermal drift to be contended with, along with adequate interstand speed matching, avoidance of camber (lateral drift), and others. The basic thickness-control equation of Hessenberg and Sims, which relates the product thickness to the roll gap and the rollseparating force (see W. F. C. Hessenberg and R. B. Sims, Principles of Continuous Gauge Control in Sheet and Strip Rolling, Proc. Inst. Mech. Engrs. 1952, vol. 166, pp. 75-81, and see also U.S. Patent No. 2,726,541), particularly in its form as modified by J. W. Wallace et al. to relate the differences in the above parameters (see U.S. Patents Nos. 2,972,268; 2,972,269; and 3,049,036), affords a satisfactory basis for accurate control in the circumstances mentioned above, but I have discovered that when it is used without further refinement as a basis for controlling a hot mill intended for processing different steels and other metals, there is an additional difiiculty, which may be overcome in accordance with the present invention. The additional difficulty is that some of the more difiicultly rollable metals such as AISI Type 316 stainless steel do not respond adequately and return to desired thickness when the roll-gap setting is decreased only in the amount predicted to be necessary by the equa tion Ah=1lm AF+AS where Ah=the change in product thickness, in. AF=the change in the roll-separating force, lb. m =the mill-spring coefficient, lb./in., and AS=the change in the roll-gap setting, in.

With such materials an additional correction is required. In accordance with the broadest aspect of the invention, I obtain the needed additional correction by modifying the electrical signal corresponding to the quantity AF so that it is relatively greater when a hard-to-roll material such as AISI Type 316 stainless steel is being rolled than it is when a steel of moderate (e.g., AISI Type 302 or Type 304 stainless steel) or little (e.g., AISI Type 430 stainless steel) difiiculty is being rolled. I have further discovered that the required correction is to some extent dependent upon the temperature of the material being rolled, so that in accordance with a more limited aspect of the invention, I provide automatic means for sensing the temperature of the work and providing the desired more accurate corresponding correction.

A complete understanding of the invention may be obtained from the following detailed description thereof, setting forth a particular embodiment thereof, with reference to the attached drawings, in which:

FIGURE 1 is a diagrammatic showing of one embodiment of the invention;

FIGURE 2 is a graph showing the temperature dependence of the hot workability of certain steels; and

FIGURE 3 is a diagrammatic showing of another embodiment of the invention.

As shown in FIGURE 1, the invention may be practiced by means of a hot-band finishing train comprising stands 2, 4, 6, 8, and 10. The slab W passes over idler rollers 12, then successively through the five rolling stands above-mentioned, and is then taken up upon a reel 14. Each of the stands 2, 4, 6, 8, and 10 has associated with it a load cell 16, a roll-position indicator 18, and a rollposition control means or screw down control 20. Screw down control 20 may be of either the fast-acting hydraulic type or of the variable-voltage type. There is also provided a product thickness gage comprising a radiation source 22 on one side of the strip W and a radiation detector 24 on the other side of said strip, adapted to emit through line 26 a signal proportionate to the amount of radiation transmitted through said strip, and hence proportionate to its thickness. The apparatus described above is conventional and forms no part of my invention.

Load cell 16, which is customarily located between the chocks of the mill stand, emits through line 28 a signal corresponding to the roll-separating force F. Line 28 leads to a differencing device 30, which is also supplied, through line 32, with a preset F signal. The preset F signal may be arrived at independently, or it may itself be generated by automatic equipment, :as for example by equipment monitoring and averaging the observed F signal until such time as the observed average becomes substantially constant, at which time the said average F is used as a preset F signal. Device 30 produces a signal that produces on line 34 a signal corresponding to the difference between the observed F signal (line 28) and the reference F signal (line 32). In accordance with prior art, the AF signal on line 34 would be fed directly to the controller 36, but in accordance with the instant invention, the AF signal is modified by being passed through a selected one or ones of the resistances 38, 40, and 42 by appropriate manipulation of corresponding associated switches or relays 44, 46 and 48. For example, with materials difficult to roll, such as AISI Type 316 stainless steel, only switch 44 would be closed. With materials of moderate difiiculty, such as AISI Type 302 stainless steel and AISI Type 304 stainless steel, only switch 46 would be closed. With material of relatively good workability, such as AISI Type 430 stainless steel, only switch 48 would be closed.

In the field of stainless steels, it is possible to classify a steels workability as good, fair, or poor, in accordance with the results of tests conducted to determine its flow stress k and its rolling friction g. The flow stress k and the rolling friction g may be determined as taught by K. Tong and G. Sachs in their article, Roll Separating Force and Minimum Thickness of Cold Rolled Strip, Journal of the Mechanics and Physics of Solids, 1957, vol. 6. The product of a flow stress k and rolling friction g gives an indication of the hot workability. For example, at 1900 F., AISI Type 430 stainless steel exhibits a workability (k-g) of 7000; AISI Types 302 and 304 stainless steel exhibit a workability of about 13,000 on the same scale, and AISI Type 316 stainless steel exhibits a workability of about 19,000 on the same scale at the same temperature.

Roll-position indicator 18 emits, through line 50, a signal proportional to the roll gap S. The line 50 leads to a differencing device 52, which is also supplied, through line 54, with a preset S signal. Device 52 emits, through line 56, an error signal AS, proportionate to the difference between signal S and the preset signal S on line 54.

A similar differencing device 58 receives a signal from radiation detector 24 indicating the thickness of the strip and a preset t signal, which is proportional to the desired thickness of the strip. From these signals, the device 58 supplies, via line 62, an error signal At to controller 36. The error signal At represents or is proportional to the difference between the actual thickness of the strip and the desired thickness of the strip.

Controller 36 may be of the same general type as the motor control (28) disclosed in Wallace US. Patent No. 2,972,268 serving to solve the equation Ah =1lmAF+AS for Ah. Whenever a detected error Ah occurs of a suitable amount (this corresponds to the preselected dead band), the error signal All is emitted, via line 64, leading to screw down control 20.

It has also been discovered that the hot workability of the steels to be rolled varies with temperature, and

accordingly, in accordance with a preferred mode of practicing the invention, the temperature of the material is sensed and taken into account. The desirability of so doing will be apparent from attached FIGURE 2, which shows the hot workability of different typical types of stainless steel at various temperatures.

Referring now to FIGURE 3, which depicts suitable apparatus for practicing the invention in this more limited aspect, the operation of all parts shown is similar to that described above in connection with FIGURE 1, with the exception that the parallel resistances 38, 40, and 42 and their corresponding associated switches or relays 44, 46 and 48 are replaced with a compensator 66, which may be a computer of the analogue type, designed in accordance with criteria which are well known in the art. Alternately, a more simplified embodiment of the compensator 66 would include parallel resistors 38, 40 and 42, each of which is supplied with a bank of resistors with associated relays. A particular relay of the bank of relays associated with the resistors 38, 40 or 42 being used is closed in accordance with the measured temperature of the slab being rolled. In this manner the AF signal is modified in accordance with both the composition and temperature of the slab being rolled. A temperature sensing device 68 is positioned near the exit of stand 8, and it emits a signal via line 70, to the compensator 66. The output of compensator 66 is a modified AF signal, emitted via line 72 to controller 36.

While I have shown and described the invention above in connection with certain embodiments, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

1. In combination with a hot-mill stand for hot-rolling metal, gage-control apparatus comprising means for producing a signal proportional to roll-separating force, means for producing a signal proportional to the roll gap, means for changing said roll-separating force signal in accordance with at least one control function consisting of the composition of the material being rolled and the temperature of the material being rolled, means for combining said changed roll-separating force signal with a signal proportional to the thickness of the material being rolled and with said roll-gap signal to produce a signal proportional to the difference between the desired workpiece thickness and the actual workpiece thickness.

2. The gage-control apparatus of claim 1 further characterized by means for adjusting the roll gap in response to said signal proportional to the difierence between the desired workpiece thickness and the actual Work-piece thickness.

References Cited UNITED STATES PATENTS 2,726,541 12/1955 Sims 7388.5 2,767,603 10/1956 Rendel 7213 2,972,269 2/ 1961 Wallace 72-9 3,111,046 11/1963 Koss 728 3,177,346 4/1965 Green 72-8 3,194,036 7/1965 Canfor 7211 3,232,084 2/ 1966 Sims 7216 CHARLES W. LANHAM, Primary Examiner.

A. RUDERMAN, Assistant Examiner, 

1. IN COMBINATION WITH A HOT-MILL STAND FOR HOT-ROLLING METAL, GAGE-CONTROL APPARATUS COMPRISING MEANS FOR PRODUCING A SIGNAL PROPORTIONAL TO ROLL-SEPARATING FORCE, MEANS FOR PRODUCING A SIGNAL PROPORTIONAL TO THE ROLL GAP, MEANS FOR CHANGING SAID ROLL-SEPARATING FORCE SIGNAL IN ACCORDANCE WITH AT LEAST ONE CONTROL FUNCTION CONSISTING OF THE COMPOSITION OF THE MATERIAL BEING ROLLED AND THE TEMPERATURE OF THE MATERIAL BEING ROLLED, MEANS FOR COMBINING SAID CHANGED ROLL-SEPARATING FORCE SIGNAL WITH A SIGNAL PROPORTIONAL TO THE THICKNESS OF THE MATERIAL BEING ROLLED AND WITH SAID ROLL-GAP SIGNAL TO PRODUCE A SIGNAL PROPORTIONAL TO THE DIFFERENCE BETWEEN THE DESIRED WORKPIECE THICKNESS AND THE ACTUAL WORKPIECE THICKNESS. 